Lab talk

Aug 25, 2010

Gold atoms assemble nanoislands on molybdenum surface

Self-assembled growth of materials could help to fabricate integrated devices on a nanometre scale. Gold islands epitaxially grown on a molybdenum surface are ideal candidates for modifying magnetic anisotropy in a deposited cobalt layer due to different coefficients of surface anisotropy at the interface between the patterned buffer and the magnetic layer.

Scientists from the Institute of Physics, Polish Academy of Sciences in Warsaw, while optimizing the structure of MBE grown magnetic multilayered systems, have found that Au deposited on a Mo(110) surface at elevated temperatures self-assembles as epitaxial islands measuring several dozen nanometres in the lateral dimension. The team suddenly realized that such a patterned buffer may spatially modify the magnetization orientation in the deposited Co ultrathin layer. The researchers found that the Co layer grown on the Au islands is magnetized perpendicularly to the film plane whereas the magnetization of the part deposited between the islands is aligned in the sample plane. As a result, the researchers have obtained an array of elevated perpendicularly magnetized dots wrapped by a trench matrix with in-plane magnetization.

A deep understanding of the island growth is desirable as the dimensions of the Au islands directly determine the size of magnetic dots. The surface energies, the mechanisms of the surface diffusion and the interlayer mass transport depending on the growth temperature as well as the amount of deposited material affect the basic parameters characterizing the Au islands, including shape, height, area and surface density. Also the relationship between the crystallographic orientations at the Mo/Au interface and the strains arising from the lattice mismatch substantially influence the island-like growth.

About the author

The group is involved in the fabrication of MBE grown magnetic layered systems and the exploration of their physical properties and structural details. The main research issues are: the modification of magnetic anisotropy by a buffer and an overlayer; patterning of the structures by self-assembly, which occurs during the growth process as well as by post-growth treatment (for example, by ion irradiation or laser beam illumination); dynamics of the magnetization reversal processes; and the interlayer magnetic coupling and the spin modification in atoms located in the vicinity of the interfaces separating the magnetic and non-magnetic layers. The investigations are carried out within the framework of the Polish National Scientific Network "ARTMAG – Magnetic Nanostructures for Spintronics".

All members of the team work at the Institute of Physics, Polish Academy of Sciences in Warsaw. Dr Andrzej Wawro is employed as an associate professor. He is a leader of the project on patterned magnetic materials supported by the Ministry of Science and Higher Education in Poland. Dr Lech T Baczewski, also employed as an associated professor, co-ordinates the activity of the network. Dr Alexei Petroutchik and Dr Piotr Pankowski are senior researchers. Marta Sobanska MSc also contributed to the work as she prepared her Masters thesis under the surveillance of Dr Andrzej Wawro.